I use a neti pot with salt water if the sore throat is from post nasal drip. Clears out the sinus cavities and shortens a cold too. Or you can have him try a salt water nasal spray like Ocean to help loosen mucous.

take fresh sage and make a tea and drink as hot as tolerable. Also, my favorite cure though gives my husband food dreams, mash garlic cloves, apply to bottom of feet. Garlic is excreted through the lungs and is antibacterial, antiviral, antifungal, and antiparasitic. So it kills the germs in the lungs as you breathe. oh yeah, rub the feet with olive oil before putting on the garlic...no accidental burns!